Lithography is a key process in the fabrication of semiconductor integrated circuits and many optical, magnetic, biological and micromechanical devices. Lithography creates a pattern on a thin film carried on a substrate so that, in subsequent process steps, the pattern can be replicated in the substrate or in another material that is added onto the substrate.
Conventional lithography, referred to as photolithography, involves applying a thin film of photosensitive resist to a substrate, exposing the resist to a desired pattern of radiation and developing the exposed resist to produce a physical pattern on the substrate. Unfortunately, the resolution of patterns produced by photolithography is limited by the wavelength of the exposing radiation. Moreover, as pattern features become smaller, increasingly expensive shorter wavelength equipment is required.
Imprint lithography, based on a fundamentally different principle, offers high resolution, high throughput, low cost and the potential of large area coverage. In imprint lithography, a mold with a pattern of projecting and recessed features is pressed into a substrate-supported moldable surface such as a thin film of polymer, deforming the shape of the film to form a relief pattern in the film. After the mold is removed, the thin film can be processed, as by removing reduced thickness portions of the film. Such removal exposes the underlying substrate for further processing such as etching, doping, or deposition. Imprint lithography can be used to replicate patterns having high resolution features in the microscale and nanoscale ranges. Details of nanoscale imprint lithography (“nanoimprint lithography”) are described, for example, in U.S. Pat. No. 5,772,905 issued Jun. 30, 1998 and entitled “Nanoimprint Lithography”. The '905 patent is incorporated herein by reference.
A potential limitation on the rate of high speed manufacturing using imprint lithography is the presence of gas between the mold and the moldable film. Pressing the mold too rapidly can entrap gas bubbles in tiny recessed regions, deteriorating the resolution of the imprinted pattern. A second limitation is the separation of the mold and the imprinted substrate. Typically, after pressing, the mold and substrate are mechanically separated from the edge by inserting a wedge between the mold and substrate. This separation from the edge usually requires that the mold and substrate be transported from the site of the pressing apparatus to the site of the separation apparatus. The separation step thus limits throughput of imprinting. Furthermore, this conventional separation may cause cracking at the edge of the mold or substrate. It thus, contributes to mold wear, increases operating cost, and limits throughput.
Accordingly, it would be highly desirable to provide methods and apparatus to permit more rapid pressing and separation in imprint lithography.